Get Raster Corner Coordinates Using Python GDAL – Step-by-Step Guide

gdalpython

Is there a way to get the corner coordinates (in degrees lat/long) from a raster file using gdal's Python bindings?

A few searches online have convinced me that there is not, so I have developed a work around by parsing the gdalinfo output, it's somewhat basic but I thought it might save some time for people who might be less comfortable with python. It also only works if gdalinfo contains the geographic coordinates along with the corner coordinates, which I don't believe is always the case.

Here's my workaround, does anyone have any better solutions?

gdalinfo on an appropriate raster results in something like this midway through the output:

Corner Coordinates:
Upper Left  (  -18449.521, -256913.934) (137d 7'21.93"E,  4d20'3.46"S)
Lower Left  (  -18449.521, -345509.683) (137d 7'19.32"E,  5d49'44.25"S)
Upper Right (   18407.241, -256913.934) (137d44'46.82"E,  4d20'3.46"S)
Lower Right (   18407.241, -345509.683) (137d44'49.42"E,  5d49'44.25"S)
Center      (     -21.140, -301211.809) (137d26'4.37"E,  5d 4'53.85"S)

This code will work on files who's gdalinfo look like that. I believe sometimes the coordinates will be in degrees and decimals, rather than degrees, minutes and seconds; it ought to be trivial to adjust the code for that situation.

import numpy as np
import subprocess

def GetCornerCoordinates(FileName):
    GdalInfo = subprocess.check_output('gdalinfo {}'.format(FileName), shell=True)
    GdalInfo = GdalInfo.split('/n') # Creates a line by line list.
    CornerLats, CornerLons = np.zeros(5), np.zeros(5)
    GotUL, GotUR, GotLL, GotLR, GotC = False, False, False, False, False
    for line in GdalInfo:
        if line[:10] == 'Upper Left':
            CornerLats[0], CornerLons[0] = GetLatLon(line)
            GotUL = True
        if line[:10] == 'Lower Left':
            CornerLats[1], CornerLons[1] = GetLatLon(line)
            GotLL = True
        if line[:11] == 'Upper Right':
            CornerLats[2], CornerLons[2] = GetLatLon(line)
            GotUR = True
        if line[:11] == 'Lower Right':
            CornerLats[3], CornerLons[3] = GetLatLon(line)
            GotLR = True
        if line[:6] == 'Center':
            CornerLats[4], CornerLons[4] = GetLatLon(line)
            GotC = True
        if GotUL and GotUR and GotLL and GotLR and GotC:
            break
    return CornerLats, CornerLons 

def GetLatLon(line):
    coords = line.split(') (')[1]
    coords = coords[:-1]
    LonStr, LatStr = coords.split(',')
    # Longitude
    LonStr = LonStr.split('d')    # Get the degrees, and the rest
    LonD = int(LonStr[0])
    LonStr = LonStr[1].split('\'')# Get the arc-m, and the rest
    LonM = int(LonStr[0])
    LonStr = LonStr[1].split('"') # Get the arc-s, and the rest
    LonS = float(LonStr[0])
    Lon = LonD + LonM/60. + LonS/3600.
    if LonStr[1] in ['W', 'w']:
        Lon = -1*Lon
    # Same for Latitude
    LatStr = LatStr.split('d')
    LatD = int(LatStr[0])
    LatStr = LatStr[1].split('\'')
    LatM = int(LatStr[0])
    LatStr = LatStr[1].split('"')
    LatS = float(LatStr[0])
    Lat = LatD + LatM/60. + LatS/3600.
    if LatStr[1] in ['S', 's']:
        Lat = -1*Lat
    return Lat, Lon

FileName = Image.cub
# Mine's an ISIS3 cube file.
CornerLats, CornerLons = GetCornerCoordinates(FileName)
# UpperLeft, LowerLeft, UpperRight, LowerRight, Centre
print CornerLats
print CornerLons

And that gives me:

[-4.33429444 -5.82895833 -4.33429444 -5.82895833 -5.081625  ] 
[ 137.12275833  137.12203333  137.74633889  137.74706111  137.43454722]

Best Answer

This can be done in far fewer lines of code 

src = gdal.Open(path goes here)
ulx, xres, xskew, uly, yskew, yres  = src.GetGeoTransform()
lrx = ulx + (src.RasterXSize * xres)
lry = uly + (src.RasterYSize * yres)

ulx, uly is the upper left corner, lrx, lry is the lower right corner

The osr library (part of gdal) can be used to transform the points to any coordinate system. For a single point:

from osgeo import ogr
from osgeo import osr

# Setup the source projection - you can also import from epsg, proj4...
source = osr.SpatialReference()
source.ImportFromWkt(src.GetProjection())

# The target projection
target = osr.SpatialReference()
target.ImportFromEPSG(4326)

# Create the transform - this can be used repeatedly
transform = osr.CoordinateTransformation(source, target)

# Transform the point. You can also create an ogr geometry and use the more generic `point.Transform()`
transform.TransformPoint(ulx, uly)

To reproject a whole raster image would be a far more complicated matter, but GDAL >= 2.0 offers an easy solution for this too: gdal.Warp.

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